Method of imaging and imaging material

ABSTRACT

In an imaging material, which normally produces upon imaging and development an image of one normal polarity (positive or negative), the trapping level is selectively controlled to produce, upon imaging and development, an image of the opposite polarity. This may be achieved, for instance, by adding a trap former to the imaging material, to produce, after selective activation of the trap former, for instance, by energy, the desired differential of the trapping levels in the image and nonimage areas. Also imaging materials comprising a trap former.

United States Patent 1191 Klose et'al.

[ June 25, 1974 METHOD OF IMAGING AND IMAGING MATERIAL 1 [75] Inventors:Peter M. Klose, Troy; Stanford R.

- Ovshinsky, Bloomfield Hills, both of 21 Appl. No.: 171,104

52 Us. 01. 96/48 R, 96/27 E, 96/48 HD, a 96/59, 96/64 151 1m. (:1. G03c5/24,.0030 5/04, 603C 5/50 [58] Field of Search 96/88, 48 R, 48 HD, 64,

[56] References Cited UNITED'STATES PATENTS 3,305,359 2/1967 Delmont96/33 Kaspaul 96/48 R Somg et al. 96/64 Primary Examiner-Ronald H. SmithAssistant Examiner-Richard L. Schilling [5 7] ABSTRACT In an imagingmaterial, which normally produces upon imaging and development an imageof one normal polarity (positive or negative), the trapping level isselectively controlled to produce, uponimaging and development, an imageof the opposite polarity. This may be achieved, for instance, by addinga trap former to the imaging material, to produce, after selectiveactivation of the trap former, for instance, by energy, the desireddifferential of the trapping levels in the image and non-image areas.

Also imaging materials comprising a trap former.

36 Claims, 8 Drawing Figures l o o o o o o o 0 o o oo o ooo o o o o o oo 0 6 6 0 o. ooooooooooo o o o o o o .o

030 ooooo-o'o METHOD OF IMAGING AND IMAGING MATERIAL The presentinvention relates to a new method for recording information and forproducing images and to new imaging materials.

The silver halide imaging system is a negative working system. In thoseareas of the image which are struck by light, a dark precipitate ofsilver is formed upon development. In order to produce positive imageseither copies must be made from the negative or the original image mustbe reversed in the development by the inclusion of a bleaching step, areversal exposure step and a second development step. Both methods arecumbersome and time consuming. Positive copies may also be produced inthe silver halide system by diffusion techniques though also this addsto the cost of the system and usually extends the access time.

The various known non-silver halide imaging systems, which are based ona great variety of chemical reactions. produceeither negative orpositive images as is inherent in the particular physical or chemicalreaction involved in the system and in the material used in the system.Generally the systems which are not based on the silver halidechemistry, cannot be adapted to a reversal development. It is thereforenot possible with these systems to reverse the polarity of the image.The user of a given system has no choice of the polarity of the imageswhich he obtains.

, Imaging systems are selected for a given imaging task on the basis ofimage quality, performance features, cost and other considerations andoften a system, which otherwise would fit all the desired requirements,is not acceptable because it produces images of the wrong polarity.Often'it is also desirable, once a system has been adopted, to produceby one and the same system images of both polarities, i.e., bothpositive and negative images as may be needed or desired, withoutadding'costly and time-consuming copying or duplicating steps orreversal steps in the development. As stated, the various commericallyused non-silver halide imaging systems do not provide for such choice ofpolarity. There is therefore a need for an imaging method, which permitschange of the polarity of the image produced by a given system withoutrequiring expensive or time-consuming additional steps and without beinglimited to the silverhalide system. The present invention provides sucha new method for producing images of a polarity which is opposite tothat normally produced by a given material or system.

In accordance with the invention, an imaging material, which is capableof producing upon exposure to imaging energy alatent image and ofproducing upon development an actual image of a first or normalpolarity, is provided with a trap former to produce, after imaging anddevelopment, an image of a polarity which is opposite to the polaritynormally produced. Stated more generally, the new method of theinvention permits, by selective control of the trapping levels in theimaging material, to produce images of the polarity which is opposite tothe one normally produced by a given system.

The term polarity as usedhereinis designating the character or contrastof the image viz. whether the image is positive or negative. It isunderstood that an image is positive, if the gradient of contrast isunder the conditions of detection in the same direction as it was in theimaging energy. Accordingly, in a negative image, the gradient ofcontrast of the image is opposite to that of the imaging energy.

The new method of the invention is generally applicable to all thoseimaging materials which are capable of forming a latent image, when theyare selectively subjected to imaging energy, and in which the latentimage can be developed by suitable developing means to form an actualimage, which may be visually detected or which may be detected by othermeans such as read-out equipment using physical phenomena such aselectromagnetic radiation, electrical energy, mechanical means or thelike. The formation of the latent image and the development of theactual image may be effected as successive steps or both the imaging anddevelopment may be carried out simultaneously in a single step byapplying the imaging energy and the means causing development at thesame time.

Depending on the nature of the imaging material and the manner in whichthe contrast in the image is generated, it is also desirable, that thedevelopment conditions are such or can be modified to be such that inthe development a change takes place in the areas, which have not beensubjected to the imaging energy, resulting in a substantial .change ofdetectable characteristics in these areas. The invention applies toimaging systems, which normally are negative working as well as tosystems which are normally positive working.

Using imaging energy, for instance light or other actinic radiation orany other suitable energy as the imaging energy, photons or other energyquanta may be absorbed by the imaging material itself or they may beabsorbed by another constituent of the imaging material such as anactivator or a senstizer, which transfers the absorbed photon energy tothe imaging material. In either case material being in a differentenergy state is formed inthe areas which have been subjected to theimaging energy. Material is formed by the effects of the imaging energy,which results in a higher or lower energy in the areas, which have beensubjected to the imaging energy as compared with the areas which havenot been subjected to the imaging energy. These different energy statesof material may be in the form of carriers such as electrons or positiveor hole carriers, or of free radicals, or the different state may berepresented by the fact that an electron is raised by the absorbedphoton or other energy to a higher level. Carriers may be represented bybroken bonds generated by the breaking of molecular chains or rings andthe like such asof chains of selenium atoms. The different energy statesmay also be represented by ions such as ionized atoms or ionized atomgroups or they may be represented by a chemical derivative of a compoundwhich is in a state of higher reactivity than the material surroundingit. In the case of organic compounds, the different state may berepresented by a broken chain or by the dangling bond generated by theomission of an atom or of an atom group or by a free radical. Carriersor free radicals or any other material being in a different energy stateor having an increased or decreased reactivity may be formed by anydesired mechanism as a result of absorption of imaging energy. Theforegoing described different or changed energy states may be providedin the imaging material itself or it may be provided in any activatorand/or sensitizer or in any other material being present in the imaginglayer.

The various forrns of energy states, of radicals, carriers or activatedmaterial which forms the latent image and which, by one or anothermechanism initiate and bring about a physical or chemical change in theimaging material for producing a change in the detectablecharacteristics of the imaging material upon development will bereferred to herein as energy carriers." It is to be understood, that theterm, energy carriers" is broader than the term carrier as it isnormally used and that the term energy carriers" includes the materialsof different energy states listed hereinbefore including any otherenergy state which is capable of forming a latent image and causing orpreventing the formation of material having changed detectablecharacteristics to form an actual image upon development.

In the course of the development of one type of the imaged materialsuseful in the method of the present invention, in normal, conventionaloperation the energy carriers forming the latent image initiate and makepossible a physical or chemical change, as the case may be, to produce anew state of the material having different detectable characteristicsfrom the detectable characteristics of the original imaging material.

Energy carriers can be trapped. Trapping may be the loss or reduction ofmobility of the energy carriers, making them incapable of moving to thesite where they can exert their effect on the physical or chemicalchange in the image areas. Trapping may also be the linking up of theenergy carrier with another material, which supplies a missing electron,or an energy carrier may take up an otherwise available electron toreplace a missing electron thereby changing the energy of the energycarrier making the energy carrier so modified incapable of initiating orcausing the physical or chemical change. Similar situations may occur inthe case of free radicals. The free radicals may link up with anotherfree radical thereby forming a neutral compound of lower reactivity,making it incapable of initiating or causing the change of detectablecharacteristics in the imaged areas. Or the free radical may link upwith another activated material to form a neutral compound of lowerreactivity, which does not initiate the desired change in the imagedareas. Likewise compounds being of higher energy and more reactive mayreact with another material to form a compound of lower reactivity whichis incapable of initiating the changes in the imaged areas. All theseand any similar event, which reduces the available energy of an energycarrier, are called herein trapping."

In accordance with the present invention, trapping levels areintroduced, preferably to the point that no energy carriers areavailable for initiation of a physical or chemical change in the areasin which no detectable change is desired. Trapping levels may beincreased in various manner, for instance by control of the temperature,by the provision of electrons, for instance, in form of an electriccurrent, or by chemical means. In accordance with the present invention,trapping levels are preferably increased by providing the imagingmaterial with another material which is capable of forming traps for theenergy carriers or which is capable of trapping the energy carriers, forinstance, in a manner as set out hereinbefore or by any other desiredmechanism. The materials added in this manner to the imaging materialare usually trap precursors or materials which directly form traps uponthe absorption of energy. All these materials are called herein trapformers. The invention provides for the introduction of trapping levels,trap precursors or trap formers of the kind as will be describedhereinafter, and which in the state, in which they are introduced to theimaging material, possess only little or no trapping ability. Theyacquire their capacity of forming a trap only after they have beensubjected to energy contained in the imaging energy or to energy whichis applied imagewise in a separate step for the purpose of activatingthe trap former. The activation of the trap former is therefore usuallyimagewise the same as the formation of the energy carriers generated bythe application of the imaging energy. The trap formers are thereforemade available in their active or trapping state usually where theimaging energy has been applied. Furthermore, for reasons to beexplained hereinafter the trap former is usually applied in a sufficientquantity, such that a substantial excess of traps will be formed overthose needed for trapping the energy carriers generated by the imagingenergy in the imaged areas.

To produce an image of opposite polarity, it is not only necessary totrap the energy carriers in the areas having received the imagingenergy, so as to suppress or prevent the taking place of the physical orchemical change which leads to the formation of the change in detectablecharacteristics in the imaged areas, but it is also required to generateenergy carriers in the areas of the image, which have not received theimaging energy, so as to produce a physical or chemical change in theseareas for the production of a change of detectable characteristics inthe areas which have not received energy. This can be readily achievedby the application of suitable development conditions. However,development is not imagewise and encompasses all areas, the areas whichhave not received the imaging energy as well as the areas which havereceived the imaging energy. Consequently, merely selecting thedevelopment conditions which produce energy carriers for the initiationof a physical or a chemical change is non-selective and not imagewise.The changes in detectable characteristics resulting therefrom wouldextend therefore all over the layer of the imaging material. No imagewould be produced in this manner.

As stated above, in the preferred embodiment of the method of theinvention, the trap former is employed in excess such that asubstantially larger number of traps is formed in the imaging step thanis needed for trapping the energy carriers formed by the imaging energy.In this manner, an excess of traps is available in the areas which havereceived imaging energy. When, in the course of development, energycarriers are generated by the development conditions, these energycarriers are trapped in the available excess of traps as soon as theyare generated. Therefore, in the areas which have received imagingenergy, no energy carriers are and no or only very few energy carriersbecome available during development, which could initiate or cause aphysical or chemical change in the imaging material. Therefore no changein detectable characteristics takes place in the areas which have beensubjected to the imaging energy.

On the other hand, in the areas which have not received imaging energy,the trap former is not activated, no traps are formed and the energycarriers generated in these areas remain free and untrapped and caninitiate or cause, by the mechanism, normal for the particular imagingmaterial, the physical or chemical change, thus producing a substantialchange in the detectable characteristics in the areas which have notreceived imaging energy. As can be readily seen, in this manner animaging material which would normally become nonreflective ornon-transparent in the areas which have received the maximum imagingenergy, and which normally remains reflective or transparent in theareas which have not received imaging energy (negative polarity)reverses its polarity. By the provision of the selectively introducedtrapping levels in accordance with the invention, the areas, which havereceived maximum imaging energy, remain reflective or transparent andthe areas which have not received imaging energy become non-reflectiveor non-transparent. Accordingly, the material has become positiveworking merely by the selective control and change of the trappinglevels.

Of course, for best operability of the method, it is desirable to selecta trap former, which does not become activated under the conditionsemployed for development and the conditions necessary for the generationof the energy carriers in the areas which have not received imagingenergy. Or, in other words, the development conditions should beselected, such that generation of energy carriers occurs under theseconditions, while the trap former is not activated to form traps underthese same conditions. This may, for instance, be achieved by usingdifferent energy forms or radiant energy of different wave lengths forimaging and development, as will be exemplified hereinafter.

The selectivity of the'method of the invention in producing images of apolarity which is opposite to normal may also be achieved in anothermanner. With certain imaging materials, the number of energy carrierswhich can be generated in a given areas is limited. Accordingly, in theimaging step sufficient imaging energy may be applied, to generate themaximum possible number of energy carriers. At the same time, theincreased amount of imaging energy generates traps in sufficient numbersfor trapping essentially all the generated energy carriers. 'As before,no energy carriers have been generated in the areas which have notreceived imaging energy. Therefore, in the development step, energycarriers can be generated in sufficient number in the areas which havenot received imaging energy, while no energy carriers are generated bythe development conditions in those areas, which have received imagingenergy, because the energy carriers precursors responding to thedevelopment energy have been exhausted in these areas. In this manner,sufficient energy carriers are available in the areas which have notreceived the imaging energy, to bring about the physical or chemicalchange for producing the change in detectable characteristics in theseareas. Essentially no energy carriers are generated by the developmentenergy in the areas which have received imaging energy, and essentiallyno change in the detectable characteristics takes place in these areas.Thus also in this case, the images of opposite polarity are produced.

The method has been described hereinbefore in connection with .a blackand white system producing merely reflective or transparent andnonreflective or hereinbefore as separate, successive steps. The methodof the invention may also be operated in such manner, that the imagingis effected at development conditions so that imaging and developmentproceed at the same time.

The generation of the energy carriers may be catalyzed by the presenceof catalysts or activators in the imaging materials. Sensitizers may bepresent, which absorb the employed imaging energy and transfer it to thecatalyst or activator materialand/or to the imaging material in a form,in which the imaging layer responds with the formation of energycarriers.

In a similar'manner, catalysts or activators and/or sensitizers may bepresent in the imaging material which are capable of absorbing imagewiseenergy and transferring it to the trap former in a form best suited foreffective activation of the trap former to form the traps. Generally, itis preferred, that the catalysts, activators, and/or sensitizersfavoring the generation of the energy carriers and of the latent imagesare not the same as'those added for the favoring of the formation of thetraps. If different materials are used for these distinct purposes, itis possible to adjust the quantity and kind of these materials to eachof these purposes, though sometimes, it is possible to use the samematerials for the catalysis of the generation of traps and of thegeneration of energy carriers. An important consideration'in thisrespect is, to select and add to the imaging material such catalysts oractivators or other materials, which catalyze or favor the generation ofthe energy carriers under the selected development conditions and whichpreferably also favor and promote the physical or chemical processleading to the change of the detectable characteristics in the areas,which have not been subjected to imaging energy.

I-Iereinbefore an embodiment of the method of the invention has beendescribed, wherein a trap former is combined with an imaging material toproduce images of a polarity which is opposite to that which is normalwith the same imaging material. Accordingly, using the imaging materialwithout the trap former, one will obtain images of normal polarity. Themethod of the invention may' also be modified in such manner, that oneand the same material is capable of producing images of either polarityas may be described or needed.

For this embodiment of the invention, one employs an imaging material incombination with a trap former as described before. Preferably, oneselects a trap former which is activated by imaging energy of adifferent kind or of a different wavelength than is required for thegeneration of the carriers. At the same time one may use differentdevelopment conditions for produc ing images of either one of thepolarities.

To produce images of the normal polarity imaging energy is used, whichdoes not activate the trap formers but which is capable of generatingcarriers in the areas subjected to the imaging energy. For developmentone non-transparent areas. The new method is capable of selects thenormal developing conditions at which substantially no energy carriersare generated and no physical or chemical changes takes place in theareas which have not received imaging energy. In the case that images ofthe opposite polarity are desired from the same imaging material imagingenergy of a kind or wavelength is used which activates the trap former.In this case development conditions are selected such that energycarriers are generated in the areas which have not received imagingenergy to produce a physical or chemical change in these areas resultingin a change of the detectable characteristics.

Thus merely by varying the nature of the imaging energy and thedevelopment conditions either a positive or a negative image may beproduced at will from one and the same material. With some imagingmaterialtrap former combinations, it is also possible to merely vary theintensity or time of energy application to either activate the trapformers or not activate them as may be desired for producing either apositive or a negative image from a given imaging material.

Other objects, advantages, and features of the invention will becomeapparent to those skilled in the art from the following description andclaims of the invention and from the attached drawings in which:

FIG. 1 is a schematical, fragmentary sectional representation of aconventional imaging structure being selectively subjected to imagingenergy through an opening in a mask and showing the latent image ofenergy carriers formed by the imaging energy.

FIG. 2 is similar to FIG. 1, showing the structure after development,with the mask removed.

FIG. 3 is a schematical, fragmentary, sectional representation of animaging structure of the invention containing a trap former and beingselectively subjected to energy through an opening in the mask andshowing energy carriers formed by the imaging energy trapped.

FIG. 4 is similar to FIG. 3 showing the structure with the mask removedat the beginning of the development step.

FIG. 5 is similar to FIG. 4, showing the structure after completion ofthe development.

FIG. 6 is an imaging structure of the invention containing a trap formeror trap precursor in form of a layer adjoining to a layer of an imagingmaterial.

FIG. 7 is similar to FIG. 6, showing the structure of FIG. 6 beingexposed through a mask.

FIG. 8 is similar to FIG. 7, showing the structure of FIG. 7, with themask removed, as it is developed by heat.

Referring to the drawings, the imaging structure shown in FIG. 1generally at 10 comprises a substrate 12 and deposited thereon a layer14 of conventional imaging material. The imaging material in layer 14may be any desired imaging material which is capable of forming, uponselective exposure to imaging energy, a latent image of energy carrierswhich upon development produces an actual image in the layer 14. Uponlayer 14 is placed a mask 16, having opaque areas 18 and transparentarea 20. Imaging energy 22, such as light, is applied through thetransparent areas 20 of the mask onto layer 14 of imaging material. Theimaging energy 22 generates in the area of layer 14 underlying thetransparent area 20 of the mask energy carriers 24, represented in thedrawings by small dots. These carriers form in the layer 14 a latentimage corresponding to the outline of transparent area 20 of mask 16.

After completion of the exposure of layer 14 to the imaging energy, themask is removed and the structure 10 subjected to suitable selecteddevelopment conditions. The energy carriers 24 forming the latent imageinitiate thereby a physical or chemical change to take place in thelayer 14 of imaging material to produce in the area 26 a change in thedetectable characteristics as indicated by the large dots 28 in FIG. 2.The areas 30 of layer 14 which were covered by opaque portions 18 ofmask 16 during exposure to the imaging energy 22 and in which no energycarriers 24 were generated remain, during development, unaltered and nosubstantial change of detectable characteristics takes place in area 30.If, for instance, layer 14 was transparent or reflective in the originalunexposed structure, and if area 26 has become, during development,opaque or nonreflective, the image represented in FIG. 2 and being theresult of the exposure of the original structure, is a negative image.This means, that the imaging material of the structure 10 is negativelyworking.

In FIG. 3 is shown an imaging structure 36 which comprises substrate 38,extended thereon a layer 40 of imaging material and placed thereon animaging mask 42 having opaque areas 44 and transparent area 46. Thelayer 40 of imaging material comprises the same, negatively workingimaging material as was used in layer 14 of FIG. 1, however in layer 40there is admixed to the imaging material a trap former (not shown) asdescribed hereinbefore. The trap former, as contained in layer 40 isinert and has as such no effect on the imaging material. When imagingenergy 48, for instance light or other electromagnetic radiation,strikes the layer 40 through the transparent area 46 of mask 42, energycarriers 50 are generated as described before in connection with FIG. 1.At the same time, the imaging energy 48 comprises a component whichselectively activates the trap former admixed with the imaging material,generating traps 52 for the carriers. The energy carriers 50 are, asbefore, represented in the drawings by small dots, the traps 52 arerepresented by circles. As the energy carriers 50 and the traps 52 areformed, the carriers 50 are trapped in the traps 52. This is indicatedin the drawings by placing the small dots representing a carrier insidethe ring representing the trap. The trap former is used in suchconcentration and selected for its ability to be activated by acomponent of the imaging energy 48 and in such manner than an excess ofthe number traps 52 over the number carriers 50 is generated at a givenexposure time. This is indicated in FIG. 3 by the representation ofrings 54, which do not contain a dot, i.e., these are available or emptytraps.

After removal of mask 42, the structure 36 is subjected to developmentconditions. The development conditions are selected such that energycarriers 56 are generated in layer 40 (FIG. 4). The carriers 56 formunder these conditions in the areas 58, which have not received imagingenergy 48 as well as in area 60, which has received imaging energy 48,and which already contains the trap-energy carrier combination 50-52 andthe empty traps 54. As the energy carriers 56 are formed by thedevelopment conditions in area 60, the energy carriers are trapped intraps 54. In areas 58, containing no traps, the energy carriers 56 arenot trapped and initiate under the development conditions a physical orchemical change in the material producing material 62 of altereddetectable characteristics in areas 58 (FIG. 5). The imaging material inarea 60 of layer 40, has, because of the trapping of the generatedenergy carriers 56, not undergone any physical or chemical change, sothat the detectable characteristics of the imaging material in area 60are essentially unchanged and identical to those of the originalmaterial. If the layer 40 in its original state, prior to exposure, wastransparent or reflective, and the imaging material in area 58 hasbecome by the development opaque or non-reflective, a positive image hasbeen produced.

This means, the structure 36 is positive working. The basic imagingmaterial used therein is originally negative working as demonstrated inFIGS. 1 and 2. The addition of the trap former has therefore resulted ina reversal of the polarity.

When the negative image was produced according to FIGS. 1 and 2,development conditions were selected such, that substantially no energycarriers were generated in areas 30, i.e., in the areas which have notreceived imaging energy. In other words, development in this instance iscarried out under normal conditions as they have been established forthe particular material.

When the positive image was produced according to FIGS. 3 to 5, usingthe same basic imaging material as was used in accordance with FIGS. 1and 2 with the addition of the trap former, the development conditionswere modified in such manner that energy carriers were generated inareas 58, i.e., in the areas which have not received imaging energy. Themanner, in which the development conditions may be changed in order toproduce energy carriers in the dark areas 58 depends on the nature ofthe development system. In the case of heat development, generallyslight to modest increase of the development temperature, and/orincrease of the development time produce the desired effeet. In the caseof development by radiant energy, increase of the intensity, change ofwave length and/or increase of the length of the development may producethe desired effect. The use of additives or other means may produce'thedesired effect. If chemical developers are used, increase of thedevelopment temperature and/or extension of the development-time and/orthe use of a different development agent or adjustment of thedevelopment medium, for example of the pH, change of buffering, or theuse of additives or other means can be used to produce the desiredeffect. In other methods of development, corresponding changes may bemade as is appropriate for the particular imaging materials used.

The embodiment of the method of the invention, wherein a negativeworking imaging material may be used to produce either negative orpositive images, as illustrated in FIGS. 1 to 5, will be exemplified byway ofan elemento-organic imaging material. In US. Pat. application Ser.No. 163,891 filed July 19, 1971 by Yew C. Chang, Stanford R. Ovshinskyand Werner W. Buechner are disclosed new elemento-organic imagingmaterials, which can be readily adapted for the purposes of the presentinvention permitting the production of positive and negative images fromthe same imaging material solely by the selective control of trappinglevels. Special reference is herewith made to said application Ser. No.163,891 and the disclosure thereof is herewith made part of the presentapplication.

In one embodiment of the method disclosed and claimed in saidApplication Ser. No. 163,891 an imaging layer containing anelementoorganic imaging compound is selectivelysubjected to imagingenergy to produce upon heat development an image as a result of achemical reaction in which theinorganic element, for instance telluriumor a metal is precipitated in its elementary form as the image former.This embodiment of the method works negative, i.e., this type ofelementoorganic imaging material is a negatively working imagingmaterial.

Using as an example the compound (I) the following results will beobtained, if the compound is used in layer 16 of FIG. 1 and layer 40 ofFIG. 3 as the imaging material, respectively.

For normal operation the compound (I) was incorporated in a binder offor instance, cyano ethylated starch together with acetophenone as acatalyst and acetone as a solvent in a manner as is described in saidapplication Ser. No. 163,891. The mixture was applied in form of a thinlayer onto a glass substrate and was air dried to result in structure 10of FIG. 1. After exposure to the radiation generated by a xenonelectronic flashgun and through a mask of transparent andnon-transparent areas, and after a heat development, a negativeduplicate of the image represented by the mask was obtained.

The experiment was repeated using the same materials except thatdimethylformamide was substituted as the solvent for the acetone. Themixture was spread out in form of a thin layer on a glass substrate asdescribed before, except that the film was only partially dried, leavinga considerable residue of dimethylformamide in the layer to representthe structure 40 in F IG. 3. After exposure to radiation through a maskas described before and after heat development at essentially the sametemperature, a positive duplicate of the image represented by the maskwas obtained in the manner illustrated in and described in connectionwith FIGS. 3 to 5. This shows, that the compound (1) representing animaging material which normally produces negative images, can producepositive images by the addition of a trap former. The only essentialdifference between the first and the second experiment was, that thelayer 40 used in the second experiment contained during the exposure bythe same energy source a relatively small amount of dimethyl formamidewhich served as the trap former. Upon exposure to the radiation trapswere selectively formed and the energy carriers formed in theilluminated areas by the radiation were trapped.

When the second experiment was repeated, using dimethyl formamide as thesolvent but removing prior to exposure substantially all of the dimethylformamide, a negative image was obtained as described in the firstexperiment.

The temperature used for development in all three experiments wasessentially the same. It would be expected that a higher temperatureshould be necessary for the generation of energy carriers or radicals bythermal means in the areas which have not been exposed to the radiation.It is believed that the dimethyl formamide which was present in thenon-illuminated areas, served as a plasticizer thereby facilitating notonly the generation of energy carriers or radicals by thermal means butalso facilitating thermal nucleation by giving greater mobility to thegenerated energy carriers and to the molecules of compound (1) and/or tothe various reaction products and intermediaries occurring in thereaction leading from the compound (I) to the precipitation ofcrystallites of tellurium. Thus, in effect, the presence of the excessof dimethyl formamide in the areas which have not been subjected to theradiation has the same effect as would otherwise have the increase ofthe development temperature. This effect is offset in the illuminatedareas by the presence of a sufficiently large excess of traps, whichimmediately trap the energy carriers or radicals as they are formedduring the heat development and therefore prevent thermal nucleation andformation of a tellurium precipitate in the illuminated areas.

The need for an excess of traps in the illuminated areas wasdemonstrated by another experiment, wherein an intermediarysubstantially lower content of dimethyl formamide was used underconditions similar to those in the second experiment. The reduction ofthe amount of dimethyl formamide and thus of the traps caused theprecipitation of tellurium in both the illumi nated and non-illuminatedareas so that no distinct image was formed, even though the developmenttemperature was essentially the same as used in the first threeexperiments.

The method of the invention may be operated in similar manners with anyof the other elemento-organic imaging materials taught and claimed insaid application Ser. No. l63,89l.

The method of the invention may also be used to produce negative imageswith an imaging material which normally produces positive images. Thisembodiment of the method will be demonstrated and exemplified by way ofan inorganic imaging system.

A structure was prepared as shown at 10 in FIG. 1 of the drawing usingas the layer 14 an amorphous material which consisted of about 95 atomicpercent selenium and about atomic percent sulfur. The layer was about0.5 micron thick. When the structure was imaged and heat developed asdescribed in conjunction with FIGS. 1 and 2 using the conditionsnonnally applied for this type of material an image was obtained whichconsisted of crystalline material in area 26 and of essentiallyamorphous material in areas 30 (FIG. 2). The imaging proceeds by amechanism in which carriers are generated, which form nucleation centersserving as the sites for crystallization in a manner as generallydescribed in conjunction with FIGS. 1 and 2. The crystalline material inarea 26 scatters light more efficiently than the amorphous material inarea 30, so that the image upon reflection viewing is positive.

ln an example demonstrating the reversal of the polarity of the justdescribed selenium-containing imaging system by the use of trappinglevels, a structure was prepared as shown generally at 70 in FIG. 6. Thestructure comprises a substrate, for instance, of glass or plastic suchas Mylar, a thin layer 74 of copper extended on the substrate 72 and alayer of the above described selenium composition comprising about 95atomic percent selenium and about 5 atomic percent sulfur. The layer 74of copper, serving as the trap precursor, may be for instance from 0.01to 0.1 micron thick and the layer of the selenium composition may beabout 0.5 micron thick. As shown in FIG. 7, a mask 78, having opaqueareas 80 and transparent areas 82 was placed onto structure 70 incontact with the layer 76 of the selenium composition. The structure 70was thereafter exposed to a 60 joule flash of an electronic xenonflashgun as indicated in FIG. 7 by arrows 84. Carriers 86, generated,for instance, as hole-electron pairs by the breaking of bonds inselenium chains or rings, are formed primarily at the interface oflayers 74 and 76. The carriers 86 are indicated as before by small dotsin the drawings. At the same time, certain energy components of theflashgun activated by the copper layer 74 to form directly orindirectly, as will be explained hereinafter, traps 88 primarily at theinterface between layers 74 and 76. Traps 88 trapped the carriers 86 asindicated in FIG. 7 by placing the dots 86 representing the carriersinto the partial circle 88 representing traps. Under the imagingconditions, a great excess of traps 90 is formed, which traps 90 areempty and do not contain any carriers. These empty traps 90 may beformed at and stay primarily at the interface between layer 74 and 76,or they may under the effect of the flash energy, migrate into theinterior of layer 76 as shown.

The mask was thereafter removed and structure 70 was heated by heatsource 92 and heat radiation 94 to about 120 C. for about 1 minute. Theselenium composition crystallized in areas 96 to form the characteristicselenium crystals 98, while essentially no crystallization occured inilluminated area 100. A negative image of highly reflective areas 96and'of a substantially amorphous surface in area 100 of low reflectivitywas formed. Areas 96 had not received the imaging energy of theflashgun. The crystallization in the nonilluminated areas is thermallyinitiated and proceeds by this mechanism. Thermally generated carriersform nucleation centers serving as the growth sites for thecrystallites. in the illuminated area, the carriers 86 formed by theradiant energy are trapped in traps 88 and any thermally generatedcarriers 91 are trapped in the empty traps 90.

As stated hereinbefore, it is also possible that the strong illumination84 has exhausted all thermally excitable carriers by light excitation,placing them into the traps already in the illumination step. In thisinstance, no more carriers can be thermally generated in the illuminatedarea during the heat development, because the material has beenexhausted of thermally excitable carriers.

Metallic copper, as it was laid down in layer 74, is not believed to bein itself the trap former. The metallic copper may form at the interfacewith the selenium and sulfur containing layer the respective selenideand/or sulfide molecules which may serve as the trap formers. When thelayer is exposed to the imaging energy, the copper selenide and/orsulfur molecules become activated forming the traps, which may berepresented by, for instance, copper ions. Additional quantities ofcopper selenide and/or sulfides may form under the effect of the imagingenergy to form instantaneously additional quantities of traps. Thereforethe deposited copper may be merely a trap precursor. It is, however,also possible that the copper is the trap former by the fact, that underthe effect of the illumination copper diffuses into the layer of theselenium composition to directly form the traps. The copper layer itselfmay also directly serve as the traps after it has been activated. It maytrap the carriers which are in the case of selenium holeelectron pairsand which may attach themselves to the copper layer thus becoming unableto move to the crystallization sites. Thus, the copper layer selectivelyprovides directly or indirectly suitable trapping levels to keep thecarriers trapped for sufficiently long times to prevent them fromforming nucleation centers and crystallization sites. The invention isnot limited in any way to any particular theory of the trap formation.

lt is also possible to admix the copper to the selenium compositioninstead of depositing it as a separate layer.

take place, as has been described above.

Other trap formers or trap precursors such as arsenic may be used, whichmay likewise be deposited as an intermediary layer in contact with thelayer of selenium imaging material or which'may be admixed to theselenium material in the layer. If desired, a silver catalyst layer maybe deposited between the copper layer 74 and the layer76 of the seleniumcomposition. The silver exerts in this case a catalytic effect, withoutinhibiting or preventing the effect of the copper layer as to itsability of selectively controlling trapping levels.

If silver is admixed to the selenium imaging material in smallpercentages of up to about 6 to 10 atomic percent depending on thecomposition of selenium layer, it acts as a catalyst, promoting thecrystallization and making possible lower illumination levels andshorter development times without reversal of the polarity of the image.If silver is admixed to the selenium composition in higher percentagesof, for instance, 10 to or more atomic percent, it acts as a trap formeror trap precursor, making possible reversal of the polarity of the imageand the forming of negative images in accordance with the method of theinvention as described hereinbefore in connection with the use ofcopper.

It is important in the method of the invention, that the imaging energycontain a component which is capable of activating the trap formers andthat it is applied in'such way and at such energy level and in suchamount, that the carriers responsible for crystal growth arepredominantly trapped in the illuminated areas. It is furthermoreimportant, that the traps are deep enough so as to prevent that theenergy employed in the development step such as heat, raise the carriersout of the traps.

The first requirement is demonstrated by an experiment, in which thestructure described in connection with FIG. 6 and comprising the copperlayer and the selenium composition was exposed to light of about 1,000foot candles from an incandescent lamp at about 120C. with a developmentof seconds. Under these conditions a positive image was obtained insteadof the negative image described in connection with FIG. 7. Thus underthese light conditions, the trap former (coper or copper derivatives)was not activated to form traps or the traps formed under theseconditions are not deep enough to hold the carriers under developmentconditions. More nuclei were formed in the illuminated area than in thenon-illuminated areas, and crystallization proceeded much more rapidlyin the illuminated areas than in the non-illuminated areas.

The second requirement is demonstrated by an experiment in which astructure as described in FIG. l was used in which the layer 14consisted of a composition of 75 atomic parts selenium and 25 atomicparts silver, Le, a composition high in silver content as vmentionedhereinbefore. The structure was subjected to the light of anincandescent light source providing about 1,000 foot candlesillumination, while it was simultaneously heated. When the heating waseffected at I provides sufficient energy, which permits the carriers toleave the traps allowing them to contribute to the growth of thecrystallites in the usual way by light-- enhanced crystal growth. At thelower development temperature of C. the heat energy is not sufficient toraise the carriers from the traps. The carriers remain trapped and thenegative imaging process proceeds in the manner as described inconnection with FIGS. 6 to 8. At some temperature intermediary between100 and C. no contrast and no image is obtained with the seleniumcomposition used for this experiment. With other imaging systems, thetrapping levels differ and usually, the traps are deep enough so thatthe development energy does not free the energy carriers. The foregoingexperiments show, that it is sometimes possible to obtain with animaging material containing a trap former an image of normal or ofreversed polarity, solely by varying the developing energy.

Hereinbefore has been demonstrated, that trapping levels can becontrolled and changed in such manner, that an image of reversedpolarity is obtained by varying among others the intensity and/or thenature of the imaging energy and/or by varying the intensity of thedevelopment energy. Trapping levelsand thereby the polarity of the imagecan also be controlled and varied by a pre-treatment given to theimaging material prior to the application of the imaging energy. Thefollowing examples demonstrate the effect of a thermal pretreatment ofan inorganic imaging material comprising a selenium composition.

Four samples I to IV of a structure as shown in FIG. 3 were prepared,wherein the substrate 38 was glass and the layer 40 of imaging materialwas a 0.5 micron thick layer of a composition of 94 atomic partsselenium, 5 atomic parts sulfur and 1 atomic part arsenic. The arsenicserves as the trap former as explained hereinabove.

Each of the samples I to IV was exposed at room temperature to a 2millisecond flash from a 60 joule electronic xenon flashgun. All sampleswere developed identically in the dark at a temperature of C., so thatexposure and development of all samples were the same. However, each ofthe samples I to IV was given a different pre-treatment prior to theexposure to the flash of the flashgun. Sample I received no thermalpretreatment. Upon flashing and development as stated above, a negativeimage was obtained as expected in accordance with the teaching of thepresent invention. Sample II was preheated by placing it for 10 secondsonto a hotplate heated to 130C. After flashing and development asdescribed above, a negative image was obtainedas in Sample I. Thisshows, that the short time of preheating (a certain time is required tobring the sample to the preheat temperature) did not change the trappinglevels. No change in the polarity was effected by the very shortpreheating treatment.

Sample III was placed on the aforementioned hotplate for 20 seconds.After flashing and development in the above described manner, a positiveimage was obtained. The thermal pre-treatment of somewhat longer timeinitiated thermal nucleation and generation of crystallization sites,thereby changing the trapping levels and causing the crystallization toproceed in normal manner, i.e., the effect of the trap formers iseliminated and no essential trapping of carriers occurs.

Sampel IV was placed on the aforementioned hotplate for 30 seconds.After flashing and development in the above described manner, a negativeimage was obtained. Sample lV therefore produced a reversed image asexpected in accordance with the teaching of the invention. Trappinglevels are high and traps generated by the arsenic are effective intrapping the carriers genereated by the light and by thermal energy inthe illuminated areas.

With other imaging materials, trapping levels may be readily controlledin a similar manner, for instance by subjecting the material to a briefpre-exposure to specific energy forms, such as electromagnetic radiationof a certain wavelength and intensity for an optimum length of time andso forth. In similar manner, a brief pre-treatment with chemicals suchas in vapor form or in liquid or in dissolved form may readily affecttrappping levels in a given imaging material. In this manner it ispossible to make a choice with these imaging materials of whether apositive or a negative image is produced. This may be simply achieved bygiving the material a short pre-exposure or briefly contacting thematerial with a chemical material without the need for altering theexposure and/or development conditions. Of course, with other imagingmaterials the choice of the polarity of the produced image may bedetermined by varying the exposure and/or development conditions as hasbeen set out and demonstrated hereinbefore.

The trapping levels may also be controlled by purely physical meanswithout the addition of a trap former. So, for instance, may thepolarity of an image in a selenium composition or other imaging materialbe controlled by the selective application of an electric current whichmay have the effect of trapping carriers or of generating carriers, sothat in effect a reversal of the polarity of the image from its normalpolarity may also be effected in this manner.

The operation of the method of the invention has been demonstratedhereinbefore by way of example with elemento-organic imaging materialsand with selenium-type imaging materials. The method may be used insimilar manner with any other suitable imaging material in which in theimaging process a latent image is formed by energy carriers, which isthereafter developed by suitable development means. Suitable imagingmaterials include the so-called memory materials which under the effectof imaging energy and development energy produce a physical change instructure to produce a change in detectable characteristics. Thesematerials which may be inorganic or organic are described and theirapplication is taught, for instance, in US. Patent 3,530,441 issued onSept. 22, 1970, to S. R. Ovshinsky and in copending application Ser. No.143,781 filed on May 17, 1971 by Robert W. Hallman and Stanford R.Ovshinsky. Special reference is herewith made to this patent and to thisapplication and the disclosure thereof is herewith incorporated into thepresent application. Examples of suitable memory materials, useful inthe present invention include besides the materials mentioned in thesaid patent and patent application various other selenium-containingcompositions including a large variety of metal selenides, such ascadmium selenides. Other materials useful in the method of the presentinvention include various sulfides such as cadmium sulfide, arsenictrisulfide and arsenic pentasulfide. Generally preferred are thosememory materials which have an energy gap of at least about 1 eV.

Other suitable imaging materials which may be used in the method of theinvention are the hereinbefore described elemento-organic imagingmaterials as well as any other suitable organic or inorganic imagingmaterials, in which the image forming mechanism involves the formationof energy carriers which are capable of being trapped in accordance withthe method of the invention.

A wide variety of trap formers may be used in the practice of theinvention. Generally one will select the trap former most suited toprovide upon activation the most effective traps. As has been set outhereinbefore, the energy carriers may have a variety of forms. The trapsbecome effective by either lowering the mobility of the energy carrieror by deactivating them, for instance, by releasing the excess absorbedenergy or by absorbing the excess absorbed energy. This may be achievedby electrical neutralization with the release of the energy, forinstance, in form of heat, by attachment of carriers to reduce theirmobility, by chemical reaction to form a more stable and less reactivecompound and so forth. In each of these instances one will select a trapformer which is most adapted to achieve the trapping event in the mosteffective manner. Of course, as explained hereinbefore, the trap formershould also be capable of being selectively activated to form thedesired active traps in the desired areas. As stated, the term trapformer as used herein includes also materials which do not directly formthe traps upon activation by the energy, but which by one mechanism oranother provide at least one constituent which eventually is part of thetrapping mechanism. These materials include the hereinbefore mentionedtrap precursors and it is understood that these materials fall under themeaning of the term trap former.

The method of the invention has been described hereinbefore as requiringa trap former, which upon activation by energy produces traps. Theinvention includes also the opposite situation, where an active materialis added to the imaging material, which is capable of serving as theactive traps. When layers of imaging material containing these activetraps are selectively subjected to imaging energy, the traps in theareas receiving the energy are deactivated and become ineffective astraps.

The method of the invention is predicated on the concept of controllingin an imaging material the trapping levels. Oftentimes, two differentenergy forms are used, one for imaging and one for development. Thetrapping levels are not only determined by the ability of an imagingmaterial of trapping the energy carriers generated in the imaging stepby the imaging energy, but it is also desirable that an excess of trapsis available for trapping the energy carriers generated by thedevelopment energy. This means also, that the trap should besufficiently deep to prevent that the trapped energy carriers arereleased under the effect of the development energy. On the other handthe traps should not be too deep so as to prevent that the imagingenergy can put the carriers into the trap. In reference to the aboverecited effects generated by the presence of the traps, this means thatthe new state of the matter achieved by the trapping of the energycarriers or the deenergized form of the energy carriers is eitherirreversible or requires for its reversal a higher level of energy thanis provided by the development energy. Or, in other words, thedevelopment energy should be of a lower in- 17 tensityor energy level,than is required for the lifting of the carrier from the trap.

So, for instance in the case, that the trapping is represented by achemical reaction the bond fonnation requires a certain amount of energyto form a less reactive compound. The energy required therefore may beprovided by the imaging energy, for instance, by an absorbed photon.Usually, a certain higher energy being 'at a levelhigher than issupplied by the development Any desired imagingenergymay be used as hasbeen established to be most beneficial for a given imaging required forthe activation of the trap former is present in the imaging energy orissupplied ina separate imaging. step in sufficientamount. Preferred isgenerally electromagnetic radiation including actinic radiation, i.e.,such radiation which-is capable ofinitiating a photographic effect inanimaging material. Other imaging energy including chemical energy,,heat',electric'currents, and sometimes mechanicalenergy may be usedprovided'they canbe applied-selectively and imagewise to the imagingmaterial: The development energy useful in the methodof. the inventionwill generally be the same as that used for the particular selectedimaging material for normal operation, though sometimes, as explainedhereinbefore, the use of a different type of energy or the use ofdifferent levels of the samedevelopment energy may be beneficial.Development energy may include chemical energy, i.e., the energyprovided inform of the reactivity of a chemical compound with theimaging material. Further included areheat, electro'magnetic energy,particle energy, electricalenergy,

mechanical energy and so forth. Generally preferred is heat because heatcan be readily controlled as .to its temperature and to the length ofapplication to produce the greatest benefits in accordance with themethod of the invention-Heat is generally also inexpensive and availablefrom inexpensive equipment, providing rapid access to the finishedimage.

The method of the invention is useful for producing any kind of a recordof retrievable information including images. Examples are photographicimages produced in the camera, duplicates of images produced byprojection or by contact printing as well as any other type of imagesincluding those produced by laser energy. The record of informationproduced by the methodof the invention may be detected by visualinspection or "by read-out meansor read-out equipment using any desiredmanner and means of read-out most suitable for a given imaging material.

Hereinbefore, the methodof the invention has been described in anembodiment, in which at least some energy carriers are generated by theimaging energy, which are thereafter trappedimagewise by the activatedtraps. It is also possible, to use imaging energy,

which merely consistsv of a form of energy, which activates the trapformer in the areas, subjected to the imaging energy, and which does notgenerate'energy car-. riers in these areas. Also inthis case, the emptytrapsformed in the areas having received the imagingenergy will trap anyenergy carriers formedby the development energy in these areas. Hereagainit is possible to use one and the same imaging material containinga trap former to produce at will images of either polarity merely byselectingfor the imaging a type of energy (such as selected wavelengthsin. case cse of electro magnetic radiation) which will either activatethe energy carriers for normal operation or which will activate the trapformers for reversed operationin accordance with the invention.

Numerous'other modifications may be made tovarious forms of theinvention described hereinwithout de parting from the spirit and scopeof the invention.

We claim:

1. A methodfor producing a recordof retrievable information comprising:

the step of providing a layer comprising an imaging material whichnormally, uponselective imagewise exposure to imaging energyanduponsubjection to development conditions generates carriers andproduces an-image of one polarity, and incontactwith the imagingmaterialatrap formerv whichis capable of forming traps for thecarriersinthe imaging material,

the step of selectively subjecting saidlayer comprising the imagingmaterial andsaid trap former imagewiseto imaging energy for controllingimage wise the trapping level in said imaging material to trap thecarriers in the area subjected tothe imaging energy, and v the step ofsubjecting the imaged layer of imaging material to developmentconditions,

thereby producing in said layer comprising the imaging material an imagewhich has the oppositepolarity of said one normal polarity.

2. The method of claim 1, in which said imaging ma.- terial is one whichis capable of producing upon the selective imagewise exposure to imagingenergy a latent image comprising energy carriers, and in which. said.trapping level in said imaging material is substantially increased,thereby trapping in those areas of the layer, whichhave received theimaging energy, the energy carriers generated by said imaging energy.

3. The method of claim 2, in which additionalenergy carriers aregenerated, when the layer of imaging material is subjected todevelopment conditions, and

wherein the trapping level is increased. sufficiently to.

trap also the energy carriers generated by the development conditions inthe areas which have receivedimaging energy, while the trapping levelinthe areas which have not received imaging energy is maintained. at a lowlevel such that the energy carriers. generated in these areas by thedevelopment conditions aresubstantially not trapped, therebycontributing during development to the formation of a detectable changein the areas which have not received imaging energy.

4. The method of claim 2, in which additional energy is non-imagewiseapplied to said layer to generate in said layer additional energycarriers, which are capable of selectively initiating under developmentconditions the change of at least one detectable characteristic in theareas of the layer which have not received imaging energy.

5. The method of claim 4, in which said additional energy is applied ina separate step.

6. The method of claim 5, in which said additional energy is appliedsubsequent to the imagewise application of the imaging energy.

7. The method of claim 1, in which said layer of said imaging materialis selectively and imagewise subjected to electromagnetic radiation.

8. The method of claim 1, in which the step of controlling the trappinglevel includes the imagewise application to said layer of energy, whichis capable of controlling said trapping level.

9. The method of claim 8, in which said energy controlling the trappinglevel and said imaging energy are applied simultaneously.

10. The method of claim 1, in which said layer of said imaging materialis selectively and imagewise subjected to actinic radiation.

11. The method of claim 1, in which said imaged layer is subjected toheat energy, thereby producing a change of detectable characteristics inthe areas of the layer which have not received said imaging energy.

12. The method of claim 11, in which the heat is applied at atemperature which is higher than the temperature required fordevelopment when an image of said normal one polarity is producedwithout the step of controlling said trapping level.

13. A method for producing a record of retrievable informationcomprising:

the step of 'providing' a layer comprising an imaging material whichnormally, upon selective imagewise exposure to imaging energy is capableof forming a latent image of energy carriers and which normally, uponsubjection to development conditions, produces an image of one polarity,

the step of providing in contact with said imaging material a trapformer which is capable of forming, upon the application of energy,traps for said energy carriers,

the step of selectively subjecting selected areas of said layercomprising the imaging material to imaging energy and to energy whichactivates said trap former to form traps in said selected areas,

the step of subjecting the imaged layer of imaging materials todevelopment conditions,

thereby producing in said layer comprising the imaging material an imagewhich has the opposite polarity of said one normal polarity.

14. The method of claim 13, in which the layer comprising the imagingmaterial is selectively and imagewise subjected to imaging energy, whichcomprises a component which is capable of activating said trap former toform imagewise traps in said layer.

15. The method of claim 13, in which an excess of traps is formed,thereby trapping in said selected areas which have received said imagingenergy the energy carriers which are generated in these areas by theimaging energy and the energy carriers which are generated in theseareas under the development conditions.

16. The method of claim 13, in which said trap former is admixed to saidimaging material.

17. The method of claim 13, in which a layer of imaging material isprovided, which comprises an elementoorganic imaging material.

18. The method of claim 13, in which said energy capable of activatingsaid trap former is selectively applied imagewise in a separate step.

19. The method of claim 18, in which a trap former is provided which isan organic material.

20. The method of claim 13, in which said development conditionscomprise the application of heat to said layer comprising an imagingmaterial.

21. The method of claim 20, in which said heat is applied simultaneouslywith the application of said imaging energy.

22. A method for producing a record of retrievable information, whichmethod comprises:

the step of providing a structure comprising a layer of a memorymaterial, which is capable of generating, upon the application ofenergy, carriers, which cause a physical change in structure of saidmemory material between at least two conditions, and in contact withsaid memory material a trap former which is capable, upon theapplication of energy, to form traps for said carriers,

the step of selectively applying to selected areas of said layer ofmemory material and to said trap former imaging energy of such intensityand pulse lengththat said trap formers become activated to fonn traps,whereby the carriers generated in said selected areas are trapped insaid traps, and

the step of applying development energy to said structure, therebycausing a physical change in structure in those areas of said layer ofmemory material, which have not been subjected to said imaging energy,and producing essentially no physical change in structure in those areasof the layer of memory material, which have been subjected to saidimaging energy.

23. The method of claim 22, in which a memory material is provided insaid layer in which the energy gap difference between said conditions isat least about 1 electron volt.

24. The method of claim 22, in which one of said conditions of saidmemory material is an amorphous state and the other of said conditionsis a crystalline state.

25. The method of claim 22, in which a memory material is provided insaid layer, which comprises selenium.

26. The method of claim 22, in which a memory material is provided insaid layer, which comprises selenium and sulfur.

27. The method of claim 22, in which a memory material is provided insaid layer, which comprises a metal selenide.

28. The method of claim 22, in which a memory material is provided insaid layer, which comprises a metal sulfide.

29. The method of claim 22, in which heat is applied as the developmentenergy.

30. The method of claim 22, in which heat is applied simultaneously withthe application of the imaging energy.

31. The method of claim 22, in which electromagnetic radiation isimagewise applied as the imaging energy.

32. The method of claim 22, in which the trap fonner is admixed to thememory material.

vided as said trap former.

36. The method of claim 22, in which silver in an amount exceeding about10 atomic percent is admixed to the memory material thereby serving asthe trap former.

2. The method of claim 1, in which said imaging material is one which iscapable of producing upon the selective imagewise exposure to imagingenergy a latent image comprising energy carriers, and in which saidtrapping level in said imaging material is substantially increased,thereby trapping in those areas of the layer, which have received theimaging energy, the energy carriers generated by said imaging energy. 3.The method of claim 2, in which additional energy carriers aregenerated, when the layer of imaging material is subjected todevelopment conditions, and wherein the trapping level is increasedsufficiently to trap also the energy carriers generated by thedevelopment conditions in the areas which have received imaging energy,while the trapping level in the areas which have not received imagingenergy is maintained at a low level such that the energy carriersgenerated in these areas by the development conditions are substantiallynot trapped, thereby contributing during development to the formation ofa detectable change in the areas which have not received imaging energy.4. The method of claim 2, in which additional energy is non-imagewiseapplied to said layer to generate in said layer additional energycarriers, which are capable of selectively initiating under developmentconditions the change of at least one detectable characteristic in theareas of the layer which have Not received imaging energy.
 5. The methodof claim 4, in which said additional energy is applied in a separatestep.
 6. The method of claim 5, in which said additional energy isapplied subsequent to the imagewise application of the imaging energy.7. The method of claim 1, in which said layer of said imaging materialis selectively and imagewise subjected to electromagnetic radiation. 8.The method of claim 1, in which the step of controlling the trappinglevel includes the imagewise application to said layer of energy, whichis capable of controlling said trapping level.
 9. The method of claim 8,in which said energy controlling the trapping level and said imagingenergy are applied simultaneously.
 10. The method of claim 1, in whichsaid layer of said imaging material is selectively and imagewisesubjected to actinic radiation.
 11. The method of claim 1, in which saidimaged layer is subjected to heat energy, thereby producing a change ofdetectable characteristics in the areas of the layer which have notreceived said imaging energy.
 12. The method of claim 11, in which theheat is applied at a temperature which is higher than the temperaturerequired for development when an image of said normal one polarity isproduced without the step of controlling said trapping level.
 13. Amethod for producing a record of retrievable information comprising: thestep of providing a layer comprising an imaging material which normally,upon selective imagewise exposure to imaging energy is capable offorming a latent image of energy carriers and which normally, uponsubjection to development conditions, produces an image of one polarity,the step of providing in contact with said imaging material a trapformer which is capable of forming, upon the application of energy,traps for said energy carriers, the step of selectively subjectingselected areas of said layer comprising the imaging material to imagingenergy and to energy which activates said trap former to form traps insaid selected areas, the step of subjecting the imaged layer of imagingmaterials to development conditions, thereby producing in said layercomprising the imaging material an image which has the opposite polarityof said one normal polarity.
 14. The method of claim 13, in which thelayer comprising the imaging material is selectively and imagewisesubjected to imaging energy, which comprises a component which iscapable of activating said trap former to form imagewise traps in saidlayer.
 15. The method of claim 13, in which an excess of traps isformed, thereby trapping in said selected areas which have received saidimaging energy the energy carriers which are generated in these areas bythe imaging energy and the energy carriers which are generated in theseareas under the development conditions.
 16. The method of claim 13, inwhich said trap former is admixed to said imaging material.
 17. Themethod of claim 13, in which a layer of imaging material is provided,which comprises an elemento-organic imaging material.
 18. The method ofclaim 13, in which said energy capable of activating said trap former isselectively applied imagewise in a separate step.
 19. The method ofclaim 18, in which a trap former is provided which is an organicmaterial.
 20. The method of claim 13, in which said developmentconditions comprise the application of heat to said layer comprising animaging material.
 21. The method of claim 20, in which said heat isapplied simultaneously with the application of said imaging energy. 22.A method for producing a record of retrievable information, which methodcomprises: the step of providing a structure comprising a layer of amemory material, which is capable of generating, upon the application ofenergy, carriers, which cause a physical change in structure of saidmemory material between at least two conditions, and in contact withsaid memory material a trap former which is capable, upon theapplication of energy, to form traps for said carriers, the step ofselectively applying to selected areas of said layer of memory materialand to said trap former imaging energy of such intensity and pulselength that said trap formers become activated to form traps, wherebythe carriers generated in said selected areas are trapped in said traps,and the step of applying development energy to said structure, therebycausing a physical change in structure in those areas of said layer ofmemory material, which have not been subjected to said imaging energy,and producing essentially no physical change in structure in those areasof the layer of memory material, which have been subjected to saidimaging energy.
 23. The method of claim 22, in which a memory materialis provided in said layer in which the energy gap difference betweensaid conditions is at least about 1 electron volt.
 24. The method ofclaim 22, in which one of said conditions of said memory material is anamorphous state and the other of said conditions is a crystalline state.25. The method of claim 22, in which a memory material is provided insaid layer, which comprises selenium.
 26. The method of claim 22, inwhich a memory material is provided in said layer, which comprisesselenium and sulfur.
 27. The method of claim 22, in which a memorymaterial is provided in said layer, which comprises a metal selenide.28. The method of claim 22, in which a memory material is provided insaid layer, which comprises a metal sulfide.
 29. The method of claim 22,in which heat is applied as the development energy.
 30. The method ofclaim 22, in which heat is applied simultaneously with the applicationof the imaging energy.
 31. The method of claim 22, in whichelectromagnetic radiation is imagewise applied as the imaging energy.32. The method of claim 22, in which the trap former is admixed to thememory material.
 33. The method of claim 22, in which the trap former isprovided as a separate layer in contact with said memory material insaid layer.
 34. The method of claim 22, in which copper is provided assaid trap former.
 35. The method of claim 22, in which arsenic isprovided as said trap former.
 36. The method of claim 22, in whichsilver in an amount exceeding about 10 atomic percent is admixed to thememory material thereby serving as the trap former.